1. Field of the Invention
The present invention relates to an organic light emitting diode display device and a driving method thereof.
2. Description of the Related Art
An organic light emitting diode display device is a display device for electrically exciting phosphorous organic compounds to emit light. The organic light emitting diode display device drives organic light emitting cells to represent images. The organic light emitting cell has characteristics of a diode and so is called an organic light emitting diode. The organic light emitting cell includes an anode, an organic thin film, and a cathode.
Generally, the brightness of the organic light emitting diode is degraded as time passes. Optical feedback, which is a technique that measures the light emitted by the organic light emitting diode in a pixel and feeds back the measurement to correct for the degradation of the organic light emitting diode, has been introduced in order to compensate the degradation of the organic light emitting diode.
For example, in a pixel circuit using optical feedback, a voltage is stored by a storage capacitor coupled between a gate and a source of a driving transistor, and a turn-on time of a control transistor coupled to the storage capacitor is controlled to represent a gray level. In more detail, data corresponding to a gray level is stored by a control capacitor coupled between a gate and a source of the control transistor, and a voltage of the control capacitor is controlled according to a light emitted from the OLED to control the turn-on time of the control transistor.
However, the turn-on time of different control transistors for the same gray level may not be uniform because of variation of threshold voltages of the control transistors, the variation being caused by non-uniformity of a manufacturing process. As such, the organic light emitting diode display device has difficulties in obtaining uniform gray level due to brightness deviations between the pixels.